Incredible experiment gives infrared vision to mice – and humans could come next

Special nanoparticles (shown in white) adhere to rods (left) and cones (right) in the photoreceptors of mice. Image: Ma et al./Current Biology

By injecting nanoparticles into the eyes of mice, scientists allowed them to see near infrared light ̵

1; a wavelength that is normally invisible to rodents (or humans). It is an extraordinary achievement that becomes even more extraordinary with the realization that a similar technique can be applied to humans.

Of all the remarkable things that mice have done over the years, this is the latest achievement described in the journal Cell today. is among the most science fiction.

A team of researchers, led by Tian Xue of the University of Science and Technology in China and Gang Han of the University of Massachusetts Medical School, modified the vision of mice so that they could see near-infrared light (NIR). in addition to their natural ability to see normal light. For this purpose, special nanoparticles were injected into their eyes, the effect lasted about 10 weeks and had no serious side effects.

A series of tests showed that the mice actually saw infrared light and no other stimuli. The researchers say that the human eye is not too different from those of mice, which leads to the fantastic prospect of applying a similar technique to humans.

Humans and mice can only see a limited area within the electromagnetic spectrum indicated by the rainbow-like band. Other animals, including birds, can see ultraviolet (UV) light. Image: Cell

Humans and mice have visual access to a limited range of the electromagnetic spectrum. The wavelength range invisible to humans is very large and therefore we can not see anything outside the so-called visible spectrum (wavelengths between 380 and 740 nanometers). Infrared radiation exists as a longer wavelength in the spectrum, ranging from about 800 nanometers to a whole millimeter. Earlier infrared are the even longer wavelengths of microwaves and radio waves.

Objects in the world, whether humans or a hot soup bowl or something that looks like an ice cube, emit infrared radiation when they radiate heat. Mammals like humans and mice can not see NIR, but we have technologies, namely night vision goggles or thermal goggles, that can turn this otherwise invisible spectrum into a format we can see. The new technique applied to mice has something similar, but instead of relying on wearable technology, scientists have become familiar with the biology of the business.

In order for mice to look beyond the usual visual spectrum, Tian and Gang developed special "upconversion" nanoparticles that function in the already existing rodent eye structures. Drops of liquid containing the tiny particles were injected directly into their eyes, where they clung tightly to the photoreceptor cells with special anchors. Photoreceptor cells – the rods and cones – normally absorb the wavelengths of incoming visible light that the brain interprets as a field of vision. In the experiment, however, the newly introduced nanoparticles converted incoming NIR to a visible wavelength, which the mouse brain could then process as visual information (in which case they saw NIR as a greenish light). The nanoparticles adhered for almost two months, allowing the mice to see both NIR and visible light with minimal side effects.

Essentially, the nanoparticles on the photoreceptor cells served as transducers or converters for infrared light. The longer infrared wavelengths were captured by the nanoparticles in the retina, which were then transmitted as shorter wavelengths in the visible light range. Thus, the rods and cones to absorb the shorter wavelengths could accept this signal and send this up-converted information to the visual cortex for processing. In particular, the injected particles absorbed NIR at a wavelength of about 980 nanometers and converted it to light in the range of 535 nanometers. For the mice, this meant seeing the infrared light as a color green. The result was similar to seeing NIR with night vision goggles, except that the mice were also able to maintain their view of visible light. As mentioned earlier, the effect was temporary and lasted several weeks. Some mice had cloudy corneas, which picked up quickly.

To prove that the method really works, Tian and Gang have done a series of tests and experiments.

For example, the pupils of injected mice were dilated upon NIR exposure, but the pupils of mice without injections were not. When exposed to NIR alone, measurements of brain electrical activity in the injected mice showed that the eyes and visual cortex were functioning as in visible light.

Behavioral tests also showed that the method worked. Mice placed in a Y-shaped water maze learned to recognize the location of a hidden platform to seek refuge, as indicated by an NIR-lit display. In tests, injected mice consistently localized the platform while the mice randomly swam around the labyrinth without injections. In another test, a box with two compartments was used: one completely dark without light and one with NIR. Mice move as nocturnal creatures towards darkness. In tests, injected mice spent more time in the dark area, whereas uninjected mice showed no preference.

"These extensive experiments leave no doubt that mice injected with infrared-sensitive nanoparticles have the ability to detect infrared light and obtain visual information from it," said Vladimir J. Kefalov, professor of ophthalmology and visual sciences Washington University in St. Louis, which was not involved in the new study, to Gizmodo.

In a press release, Tian said that the nanoparticles adhered to both rods and cones and were activated by the near infrared light. Therefore, "we believe that this technology will also work in the human eye, not only for generating super vision, but also for therapeutic solutions to red vision deficiencies of human vision. "In an interview with Cell, he went on to say:

Unlike mice, humans and other primates have a structure called retinal fovea, which mediates the high visual acuity of central vision. In the human fovea, the density of the cones is much higher than that of the rods; While the number of rods in the mouse retina predominates everywhere … Because cones have different light sensitivity in spectrum and intensity compared to rods, we may need to fine-tune the UCNP emission spectrum to more efficiently activate a particular cone type humane.

As Tian noted, treatment for humans would have to be modified to work, but the new experiment suggests that it is within the realms of possibility. Kefalov said that the potential to apply a similar concept to humans is both real and exciting, but he warned that we still have a long way to go.

"The authors show that a one-time injection of nanoparticles has no long-term detrimental effects on the retina of mice," said Kefalov. "However, it is unclear whether achieving a practical infrared view in humans requires repeated injections and, if so, whether such chronic treatment has a negative impact on the structure and function of our eyes."

Acquiring capacity to see infrared light seems like Science fiction and the stuff of transhumanistic fantasies (raises the hand) would undoubtedly be a useful feature. We can see a variety of things outside our normal field of vision – and we effectively have an integrated night vision. As Tian told Cell:

People have been trying to develop a new technology to enable abilities beyond our natural abilities. Visible light, which can be perceived by man's natural vision, occupies only a very small part of the electromagnetic spectrum. Electromagnetic waves that are longer or shorter than our visible light provide much more information … Depending on the material, an object may also have different NIR absorption and reflection. We could not recognize this information with our naked eyes.

Another cool thing about this potential improvement is that no one has to carry cumbersome and energy-intensive equipment, such as B. the above-mentioned night vision goggles. It also does not require genetic manipulation. The military will most likely be interested in this work.

Dayong Jin of the School of Mathematical and Physical Sciences at the University of Technology, Sydney, described the new work as "very innovative and inspiring." Dayong, who was not involved in the study, said to his best wishes, "This work is the first demonstration of implantable and" portable "optical nanodevices." He said it was important that no inflammation or cell death was observed in the mice, but it is possible that some cells suck the nanoparticles, a view "This deserves some more detailed research."

Likewise, Kefalov was impressed by the research and said: "The authors have done amazingly good work and have characterized the effects of injecting infrared-sensitive nanoparticles on the visual function of mice, pioneering an ingenious and powerful way to improve the ability of the visual system to detect light outside the natural visible range "He believed that this was amazing" that the nanoparticles did not seem to interfere with the normal function of photoreceptors in visible light.

The question is whether the technique can be used to correct vision disorders such as color blindness less clear.

"As the procedure on the alleged Because of the ability of photoreceptors to detect and amplify light signals, the use of this approach to overcome impaired photoreceptor function requires the development of additional steps beyond the detection of light outside the visible range, "Kefalov told Gizmodo

Looking Looking to the future, Tian and Gang want to improve the technology with organic-based nanoparticles consisting of FDA-approved compounds, which can lead to even brighter infrared vision. They would also like to optimize the technique in order to better adapt it to human biology. Optimistic about this technology, Tian and Gang have already applied for a patent related to their work.

I can already imagine the television advertisement: "Ask your doctor if Nahsicht is suitable for you."